<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<h1 id="elemId">Welcome to W3Docs</h1>
<script>
elemId.addEventListener("welcome", function(event) {
alert(event.detail.name);
});
elemId.dispatchEvent(new CustomEvent("welcome", {
detail: {
name: "W3Docs"
}
}));
</script>
</body>
</html>